Originally Posted by Luthier Atlanta
Follow the above directions, but wipe down with alcohol and a old T-Shirt. Use a plastic paint, you shouldn't need a primer.
I'd be careful with alcohol. I ruined a guard off an old j bass trying to wipe it down with denatured alcohol. it was tort and the alc melted the top skin on it. It got all gummy and put off a really strong solvent like chemical odor. When it dried it was all messed up where I'd tried to rub it and had a thick dull whitish haze on the whole thing. I sanded on it for a while with 120 and it kinda sorta got OK to paint, but would have needed another good pass with some 180 or 240 to get slick enough for paint.
If you have more modern plastic guard, just scuff it with a scotchgurd pad, wipe it was a DAMP paper towel, give it a while to dry, then build a few light coats and see what you have. If it looks good shoot a couple more and call it good. If it has some rough spots hit it with wet 400, wipe it clean, let it dry and put on a couple~three more coats and see what you got.
All the priming and clear coating is overkill. use the color you want it to do the whole thing and you'll have less total paint thickness which on plastic will mean less chance of cracking and/or peeling off. Use a paint made for plastic as it will be more flexi than your standard rattle can paint, again, less chance of cracking and/or peeling.